Dispensing container with follower discharge assistant

ABSTRACT

A plastic piston and tubular container for dispensing semisolids, such as ice cream and the like. The piston has a flat, flexible, obturating wall; a depending peripheral skirt or flange, proportioned to guide the piston axially along the tubular container, with a flared lower edge to provide a fluidtight seal; and a central tubular hub, corrugated to provide radial flexibility, for connecting either a rodlike or tubular push device to the piston.

United States Patent Paul W. Stump North Olmsted, Ohio;

Charles D. W. Thornton, Stamford, Conn.; Roland C. Gardner, Bay Village, Ohio 865,915

Oct. 13, 1969 July 27, 197] Cleveplk Corporation Cleveland, Ohio [72] Inventors [21 Appl. No. [22] Filed [45] Patented [73] Assignee [S4] DISPENSING CONTAINER WITI-I FOLLOWER DISCHARGE ASSISTANT 8 Claims, 5 Drawing Figs.

52 us. Cl 222/386 [51] Int. Cl 867d 5/42 501 Field of Search 222/326,

[56] References Cited UNITED STATES PATENTS 2,090,111 8/1937 Greveling 222/386 2,529,424 4/1950 Seigh........ 222/562 2,941,699 6/1960 Schmidt et al. 222/3865 X 3,070,224 12/1962 Robinson et a1 222/3865 X 3,250,443 5/1966 Abbott, Jr. 222/3865 X 3,315,847 4/1967 Trumbull 222/327 Primary Examiner-Samuel F. Coleman AttorneyWatts, Hofi'mann, Fisher & Heinke ABSTRACT: A plastic piston and tubular container for dispensing semisolids, such as ice cream and the like. The piston has a flat, flexible, obturating wall; 3 depending peripheral skirt or flange, proportioned to guide the piston axially along the tubular container, with a flared lower edge to provide a fluidtight seal; and a central tubular hub, corrugated to provide radial flexibility, for connecting either a rodlike or tubular push device to the piston.

PATENTEB JUL27 I97! IN VENTOES STUMD 0W. THORNTON PA UL W. CHAQLEfi mm ATTOQNEYE.

LAND C. (menus/2 Wan, Q/

DISPENSING CONTAINER WITH FOLLOWER DISCHARGE ASSISTANT This invention relates to dispenser containers, especially of the type used to contain and dispense semisolid materials; and to an improved piston therefor.

Semisolid materials, such as ice cream and the like, are marketed in cylindrical paperboard tubes from which the material is dispensed at one end by a piston or plunger moved from the other end, typically by a stick. Such containers, when used to market ice cream, usually hold a single serving, which is consumed directly from the container as the piston is progressively advanced to expel the product form the tube. Because of the relatively small quantity and low cost of the product marketed in each container, the cost of the container itself must be relatively low. Heretofore, a paperboard disc with a central.

hole and metal eyelet has been used as a piston and a wooden stick with a tapered end forced into the metal eyelet has been used as a pusher to advance the paperboard disc along the tubular container to expel the product. This construction has not proved satisfactory in all respects.

One source of trouble in prior devices and a cause of production losses during filling has been the tendency of paperboard discs to move from an initial assembled position in the tube before the tube is filled. In fact, at times the discs have fallen completely out of the container tube during shipment or handling. Additional problems have been caused by variations in stick diameter. The stick diameter is somewhat critical if the stick is to be effectively connected to the disc by a force fit into the metal eyelet and if it is to effectively transmit force to advance the disc. In use, excessive force must sometimes be applied to the stick to dispense the contained material, e.g., if ice cream in a dispenser is frozen quite hard. This can cause an undersized stick to slide further through the eyelet instead of moving the disc. Another problem is that while the product is being dispensed and consumed a certain amount of melting occurs and the melted product tends to flow past the paper disc and out the bottom of the tube.

The present invention overcomes the above-mentioned and other disadvantages of the prior art devices with a novel and improved construction of a dispensing piston for containers of the type described, which is inexpensive to manufacture and which facilitates rapid and automatic assembly of the piston, push device and tube.

. A preferred piston embodying the present invention includes a wall for obturating a tubular container, which obturating wall has a smooth, preferably flat, top surface or face; a depending peripheral skirt or flange extending rearwardly from the obturating wall, proportioned to guide the piston axi-' ally within a container tube so thatit does not become skewed therein, and having an outwardly flared lower edge that forms a fluidtight seal against the tube wall and which retards sliding of the piston in the reverse direction to that for dispensing; and a central hub extending rearwardly from the obturating wall and surrounded by the peripheral skirt, for receiving and frictionally retaining a stick or tube used to push the piston for dispensing a product from the container. The piston is typically inserted into an open-ended tube and a push device is attached to the hub, by the container manufacturer. So assem' bled, the container is shipped to a product manufacturer who then fills the tubular container with the product to be dispensed, such as ice cream or the like. By virtue of the piston and tube construction, the tube, piston and push device ai'e readily maintained in assembled condition during such shipment to a product manufacturer.

Advantageously, the piston is made from plastic, which provides inherent flexibility and resiliency, and which retains its initial dimensions and strength under varying conditions of hu midity and temperature, to which the piston is subjected during manufacture, shipment, and use. In contrast, pistons of paperboard materials, which expand or contract and change in strength with varying conditions of humidity, can be troublesome to assemble and use and often become disassembled during shipment. Materials that become brittle when subjected to low temperatures, such as freezing temperatures, are subject to breakage and do not perform as well as a slightly flexible piston and are therefore also unsatisfactory. Because of the flexibility of the obturating wall of the present piston, pressure applied through the hub causes the obturating wall to dome upward, relieving tension against the inside wall of the tubular container about the obturating wall, so that the piston readily slides within the container. The slight outward flare at the lower edge of the piston skirt maintains an effective seal against the inner wall of the tubular container during such sliding. The flared skirt also serves to retain the piston within the tube by not only resisting sliding movement in a reverse direction to that in which the piston moves during dispensing, but also by abutting an inwardly directed peripheral burr at either end of the tubular container in the event the piston tends to move beyond the ends of the container.

The central hub of the piston is tubular in construction, open at the extending end, and axially corrugated. This construction, along with the inherent qualities of the plastic material, provides a hub that is flexible and resilient peripherally, so that it will expand or contract to receive push devices of either the stick or tube type, will accommodate variations in the diameter of such devices, and will securely retain the push device in place with a friction fit once the stick or tube is forced into or around the hub. The central hub extends from the obturating wall a distance beyond the orientation of the piston in automatic machinery used to assemble the piston with a push device. Thus, the direction in which the piston is facing can be readily determined by the presence of the centralhub.

Accordingly, an object of this invention is to provide an improved piston for use with a dispensing container for semisolids, such as ice cream and the like, which is inexpensive, retains its dimensions under varying conditions, which is maintained in proper relationship within a tubular container, which provides an effective seal with the walls of a container while being readily slidable therein, which accommodates stick-type or tube-type push devices, and which facilitates automatic assembly of parts.

The above and other objects, features and advantages of this invention will become more apparent from the following detailed description, when considered in connection with the accompanying drawings, in which:

FIG. I is a side elevational view, with parts in section, of a dispenser embodying the present invention;

FIG. 2 is a side elevational view, with parts in section, similar to FIG. 1, but illustrating the manner in which a piston of the dispenser distorts when pressure is applied to dispense material from the container;

FIG. 3 is a fragmentary sectional view of the dispenser of FIG. 1, illustrating structural details of the piston and tube;

FIG. 4 is a perspective view of the piston of FIG. I, illustrating constructional details of the hub; and

FIG. 5 is a side elevational view of a piston embodying the present invention, indicating certain dimensional features.

With reference to FIG. 1, a dispenser-container suitable for packaging semisolids, such as ice cream, is indicated generally at 10. The dispenser 10 includes a cylindrical paperboard tube 12 for containing semisolid material, a plastic piston 14 slidable within the tube 12 for dispensing material from the tube, and a piston actuator, i.e., a push device 16, such as a wooden stick or the like secured to the piston and extending from one end of the tube, for sliding the piston within the tube.

The paperboard tube 12 is preferably helically wound of a plurality of plies, the inner ply of which is treated or is of a material that is moisture resistant and suitable for containing a semisolid material, such as ice cream or the like, intended to be packaged. The tube 12 is typically manufactured by conventional techniques in a continuous length, which is cut to suitable sizes. When the tube is cut, an inwardly directed burr is formed at opposite ends. A burr 20 at the lower end of the tube 12 is shown in FIG. 3.

The plastic portion 14 is preferably of one-piece or integral construction, and is most suitably injection molded of high density polyethylene, which is flexible, resilient, tough, retains its dimensions and does not become brittle at relatively low temperatures to which the dispenser may be subjected, as when it is used to contain ice cream. The piston 14 includes an obturating wall 22 corresponding in diameter to the inside diameter of the paperboard tube 12 so that it fits tightly within the paperboard tube. The obturating wall 22 has a normally flat or top surface 220 and a lower surface 22b that is preferably stepped to provide a circular central portion 22c that is thicker (e.g., twice as thick) than the major surrounding portion of the wall to strengthen the central area and provide a strong base for the piston actuator. On the whole, the wall 22 is thin enough to be flexible so that it will bow or bulge upwardly, as illustrated in FIG. 2, when axial force is applied at a central location. This bulging of the wall 22 reduces the peripheral pressure between the wall 22 and the tube 12 so that the piston will more easily slide in the tube. It also facilitates assembly of the piston and tube by making insertion of the piston into the tube easier. Because the wall is normally flat, dispensing pressure immediately bows it to a convex configuration, at once reducing the peripheral frictional force on the piston. When the piston is constructed of a material such as high density polyethylene, the obturating wall 22 is sufficiently flexible to permit adequate bulging when the diameter d (as indicated in FIG. 5) of the wall is on the order of 50 to 100 times the average thickness t of the wall.

A peripheral skirt or flange 26 extends rearwardly from the obturating wall 22 relative to the direction of dispensing movement of the piston 14 in the cylindrical tube 12. The peripheral skirt or flange 26 is continuous and essentially at right angles to the obturating wall, providing a cylindrical guiding portion of the piston 14, which slides in general contact with the inside surface 12a of the tube 12. The length of the skirt or flange is sufficient to prevent skewing of the piston within the tube. For this purpose, it has been found that the ratio of the diameter d of the obturating wall 22 relative to the length L of the skirt or flange 26 should be between 4 and 4.5 to 1. A flange of shorter relative dimensions does not adequately prevent skewing of the piston, whereas a flange of longer dimensions is wasteful both of the material of which the piston is made as well as of the length of the cylindrical tube 12 needed to contain a given volume, since the piston is totally contained within the tube and, as shown in FIG. 1, detracts from the volume available for the product. Also, in general, the shorter the flange or skirt, the smaller is the resistance to sliding of the piston within the tube.

Although the peripheral skirt or flange 26 is generally cylindrical, it terminates in a slight outward curve or flare 28, best shown in FIG. 3. This curved or flared terminal portion serves as an effective seal between the inner surface 120 of the wall of the cylinder paperboard tube 12 and the piston 14, especially when pressure is applied to the piston 14 through the push device 16, as will be described in more detail subsequently. In addition, the flare 28 cooperates with the burr at the lower end of the tube 12 to maintain the piston 22 within the tube once it is inserted. As a result, any tendency of the piston to slide from the tube 12, as during shipment or loading of the dispenser, is resisted. The larger diameter and flexibility of the flared portion assures a tight, sliding, seal between the piston and tube, which prevents leakage past the piston and eliminates the need for a critical piston fit within the tube. The flare or flange portion is of sufficiently larger dimension than the diameter of the skirt or obturating wall to cooperate with the burr 20 of the tube notwithstanding variations in piston or tube diameter within manufacturing tolerances. More specifically for optimum results, the diameterfof the flared portion 28 (as shown in FIG. 5) at the lower end of the peripheral skirt or flange 26 should be at least 0.005 inchgreater and not more than 0.020 inch greater than the diameter d of the obturating wall 22, when flat. By way of a specific example, in a piston in which the diameter of the obturating wall 22 and flange 26 is 1.630 inches, the diameter of the curved or flared portion 28 is preferably 0.009 to 0.0l8 inch greater.

A central hub 32 extends rearwardly from the obturating wall 22, in the same direction as the flange 26. The hub 32 extends at a right angle from the plane of the obturating wall 22 and is tubular in shape, one end 32a being located at the back surface 22b of the obturating wall, centrally of the thicker portion 22c, and the other end 32b extending therefrom and being open. The thicker portion 220 of the wall 22 inhibits tearing or breaking of the hub from the wall 22 when nonaxial forces are applied through the push device. As shown, the hub is of generally uniform cross section in its axial direction, i.e., in radial planes, except for a slight chamfer at the inside edge of the open end 32b. A push device such as a rod or stick of the type indicated at 16 can be received within the hub or a tubular push device (not shown) can be received about the hub. The hub is sufficiently long to securely retain the push device to the piston and to hold it at generally right angles to the obturating wall 22. The tubular hub is shaped to flex, i.e., expand or contract, peripherally and is resilient so that it tends to return to its original, formed, shape. Thus, the hub can be stretched as by a rod or stick inserted into the hub, or can be compressed, as by a tube that surrounds the hub, and due to its resilience will frictionally retain the rod, stick or tube in place. The hub will also accept minor variations in the diameter of the rod, stick or tube due to this flexibility. The thickness of the obturating wall 22 at the inner end 32a of the hub is preferably equal to or slightly greater than that of surrounding portion 220, and hence is typically two to three times as thick as the major portion of the wall 22, to withstand axial dispensing pressures applied at that location by a sticklikc push device.

In the preferred construction shown, the hub 32 is corrugated axially to provide for peripheral expansion or contraction and also extends from the inner surface 22b of the obturating wall 22 a distance greater than that of the flange 26. While one particularly suitable type of corrugation is shown in FIG. 4, in which rounded axially extending depressed portions 33 extend radially inward between axially extending convex portions 34 of somewhat greater peripheral extent, other types of corrugations, pleats, or the like are also contemplated which will provide for peripheral expansion and contraction of the tubular hub. By extending a greater distance than the flange, the hub serves to indicate the orientation of the piston. That is, if the piston is placed against a flat surface, resting on either its top surface 220 or on the lower edge of the flange 26, it can be readily determined which side is facing or contacting the flat surface by the disposition of the piston. The piston will lie flat if resting on its outer surface 22a, but will be somewhat askew if. resting on the peripheral flange 26 and the outer end 32b of the hub. This feature is utilized with automatic machinery to be certain that the piston 14 is properly oriented in the machinery that inserts or secures the push device 16 to the piston 14.

It is most advantageous to form the piston 14 as a monolithic or integral member entirely of plastic, by injection molding. However, alternative constructions are contemplated. For example, the obturating wall 22 and flange 26 can be molded of one piece and a separate hub member can be attached. Such a hub member can be of metal or plastic and can be extruded in a corrugated shape or can be fabricated by deforming a cylindrical tube to form axial corrugations and thereafter cutting the extruded or formed tube into lengths corresponding to the length of the hub desired. Hubs constructed in this manner are then welded or adhesively attached to the inner surface 22b of the obturating wall 22 or, if provided with a suitable groove or undercut, can be snapped into an aperture that can be provided in the piston for this purpose.

Typically, the dispenser 10 is fabricated by a container manufacturer and shipped in assembled condition to the manufacturer of the material to be packaged. The container manufacturer will form the piston 14, attach the push device 16 and assemble the piston 14 within the tube 12. Because of the burr on the end of the tube 12 and the slight outward curve or flare at the base of the skirt 26, the piston 14 is securely retained within the tube 12 once it is forced through an open end of the tube. This is true even if dimensional tolerances have resulted in a relatively free fit between the obturating wall 22 and the cylinder 12 or if the cylinder has changed dimensions, due to changes in the environment, especially changes in humidity. Thus, this construction overcomes a serious disadvantage of known dispenser containers of this general type in which the piston and push device often became separated from the tubular container during shipment.

Once the container is filled with semisolid material, such as ice cream or the like, the dispenser is ready for use. During use, the semisolid material is dispensed through the upper end of the tube 12, in the orientation of FIG. 2, by moving the push device 16 and piston 14 upward, in the direction of the arrow. Because the obturating wall 22 is flexible, upward pressure exerted by the push device 16 at the center of the obturating wall tends to bow the wall convexly upward, as shown in FIG. 2.' This, in tune, tends to relieve the pressure between the piston and the tube 12 at the periphery of the obturating wall, i.e., at the juncture of the extending flange or skirt. Once the pressure is relieved, the friction between the. tube and piston is reduced and the piston tends to slide relatively easily within the tube 12, facilitating the dispensing of the material. At the same time, the outward curve or flare 28 at the base of the skirt 26 maintains a liquidtight seal between the inner surface 120 of the tube 12 and the piston. As a result, even if the product is or has become very flowable, there will be no appreciable leak-through past the piston 14.

- From the preceding description of a preferred embodiment of this invention, it will be apparent that the advantages and features referred to have been achieved and a novel piston and tubular container for dispensing semisolids has been provided. It should also be understood, that while a preferred embodiment of this invention has been described in detail, modifications or alterations may be made therein within the scope and spirit of the invention.

What we claim is:

1. A molded plastic piston of unitary construction for-use in tubular dispensers comprising: a circular flexible obturating wall with a flat outer or front surface deformable outwardly, i.e., forwardly, under force applied centrally thereof; generally cylindrical flange or skirt integral with the obturating wall at the circumference thereof and extending away from the wall in only a rearward direction from the top surface, and adapted to slide within a tubular member and properly orient the obturating wall therein, said flange or skirt abruptly increasing in outside diameter at a location remote from the wall and terminating in a circumferential portion the outside diameter of which is greater than that of the obturating wall and major portion of the flange or skirt to provide a sliding seal at the end of the flange or skirt between the piston and a tubular dispenser; and a central hub integral with and extending rearwardly from the obturating wall for securing the end of a push member to the piston.

2. A piston as set forth in claim 1 wherein the pistonis made of high density polyethylene, and the diameter of the obturating wall is on the order of 50 to 100 times as great as the average thickness of the wall to provide sufficient flexibility so that the wall will dome when pressure is applied at the hub during use.

3. A piston as set forth in claim 1 wherein the diameter of the obturating wall is between 4 and 4.5 times as great as the axial length of the skirt or flange.

4. A piston as set forth in claim 1, wherein said circumferential portion is formed by an outward curve or flare of the flange or skirt.

5. A pistonas set forth in claim 4 wherein the outward curve or flare of the skirt is small, being not more than 0.020 inch greater in diameter than the obturating wall when the top surface of said wall is in a flat condition.

6. A molded plastic piston of unitary construction for use in tubular dispensers for ice cream or the like, comprising: a circular flexible obturating wall with a flat outer or front surface deformable outwardly, i.e., forwardly, under force applied centrally thereof; a generally cylindrical flange or skirt integral with the obturating wall at the circumference thereof, forming a peripheral junction therewith that has a rounded transverse contour, extending away from the wall in only a rearward direction from the top surface, and adapted to slide within a tubular member and properly orient the obturating wall therein, said flange or skirt abruptly increasing in outside diameter at a location remote from the wall and terminating in a circumferential portion the outside diameter of which is greater than that of the obturating wall and major portion of the flange or skirt to provide a sliding seal at the end of the flange or skirt between the piston and a tubular dispenser; and a central hub integral with and extending rearwardly from the obturating wall for securing the end of a push member to the piston; said obturating wall having a central area extending radially beyond said hub and terminating short of said annular flange or skirt that is of greater thickness than the remainder of said wall.

7. A piston of unitary construction for use in tubular dispen sers for ice cream or the like comprising: a circular flexible obturating wall with a flat outer or front surface, deformable outwardly, i.e., forwardly, under force applied centrally thereof, to facilitate sliding of the piston within a tubular member; a flange or skirt integral with and extending from the obturating wall at the circumference thereof in a rearward direction and having a major cylindrical portion adjacent the obturating wall that, at a location remote from said wall, steeply or abruptly increases in diameter to an enlarged circumferential portion, said skirt being adapted to fit in slidable relationship within a tubular member and properly orient the obturating wall therein, and said enlarged circumferential portion being adapted to provide a sliding seal between the flange or skirt and the piston and tubular member; and a central hub extending rearwardly from the obturating wall for securing the end of a push member to the piston.

8. In combination, a tubular container and a piston within said container, said container having an open end with an inwardly extending peripheral burr that reduces the size of said open end with respect to the inside cross-sectional dimensions of the container, and said piston having a circular flexible obturating wall with a normally flat outer or front surface deformable outwardly, i.e., forwardly, under force applied centrally thereof, a central hub extending rearwardly form the obturating wall, and a peripheral skirt or flange integral with and extending from the obturating wall at the circumference thereof in a rearward direction and having a major cylindrical portion adjacent the obturating wall that, at a location remote from said wall, steeply or abruptly increases in diameter to an enlarged circumferential end portion, said skirt or flange being slidably received within the container, and the circumferential end portion being more readily movable past said burr in a direction of movement in which the skirt or flange follows the obturating wall, as when the piston is inserted obturating-wall-first into said open end, than in the opposite direction, in which movement of the piston is substantially obstructed by said burr to inhibit removal of the piston from the container. 

1. A molded plastic piston of unitary construction for use in tubular dispensers comprising: a circular flexible obturating wall with a flat outer or front surface deformable outwardly, i.e., forwardly, under force applied centrally thereof; a generally cylindrical flange or skirt integral with the obturating wall at the circumference thereof and extending away from the wall in only a rearward direction from the top surface, and adapted to slide within a tubular member and properly orient the obturating wall therein, said flange or skirt abruptly increasing in outside diameter at a location remote from the wall and terminating in a circumferential portion the outside diameter of which is greater than that of the obturating wall and major portion of the flange or skirt to provide a sliding seal at the end of the flange or skirt between the piston and a tubular dispenser; and a central hub integral with and extending rearwardly from the obturating wall for securing the end of a push member to the piston.
 2. A piston as set forth in claim 1 wherein the piston is made of high density polyethylene, and the diameter of the obturating wall is on the order of 50 to 100 times as great as the average thickness of the wall to provide sufficient flexibility so that the wall will dome when pressure is applied at the hub during use.
 3. A piston as set forth in claim 1 wherein the diameter of the obturating wall is between 4 and 4.5 times as great as the axial length of the skirt or flange.
 4. A piston as set forth in claim 1, wherein said circumferential portion is formed by an outward curve or flare of the flange or skirt.
 5. A piston as set forth in claim 4 wherein the outward curve or flare of the skirt is small, being not more than 0.020 inch greater in diameter than the obturating wall when the top surface of said wall is in a flat condition.
 6. A molded plastic piston of unitary construction for use in tubular dispensers for ice cream or the like, comprising: a circular flexible obturating wall with a flat outer or front surface deformable outwardly, i.e., forwardly, under force applied centrally thereof; a generally cylindrical flange or skirt integral with the obturating wall at the circumference thereof, forming a peripheral juncture therewith that has a rounded transverse contour, extending away from the wall in only a rearward direction from the top surface, and adapted to slide within a tubular member and properly orient the obturating wall therein, said flange or skirt abruptly increasing in outside diameter at a location remote from the wall and terminating in a circumferential portion the outside diameter of which is greater than that of the obturating wall and major portion of the flange or skirt to provide a sliding seal at the end of the flange or skirt between the piston and a tubular dispenser; and a central hub integral with and extending rearwardly from the obturating wall for securing the end of a push member to the piston; said obturating wall having a central area extending radially beyond said hub and terminating short of said annular flange or skirt that is of greater thickness than the remainder of said wall.
 7. A piston of unitary construction for use in tubular dispensers for ice cream or the like comprising: a circular flexible obturating wall with a flat outer or front surface, deformable outwardly, i.e., forwardly, under force applied centrally thereof, to facilitate sliding of the piston within a tubular member; a flange or skirt integral with and extending from the obturating wall at the circumference thereof in a rearward direction and having a major cylindrical portion adjacent the obturating wall that, at a location remote from said wall, steeply or abruptly increases in diameter to an enlarged circumferential portion, said skirt being adapted to fit in slidable relationship within a tubular member and properly orient the obturating wall therein, and said enlarged circumferential portion being adapted to provide a sliding seal between the flange or skirt and the piston and tubular member; and a central hub extending rearwardly from the obturating wall for securing the end of a push member to the piston.
 8. In combination, a tubular container and a piston within said container, said container having an open end with an inwardly extending peripheral burr that reduces the size of said open end with respect to the inside cross-sectional dimensions of the container, and said piston having a circular flexible obturating wall with a normally flat outer or front surface deformable outwardly, i.e., forwardly, under force applied centrally thereof, a central hub extending rearwardly from the obturating wall, and a peripheral skirt or flange integral with and extending from the obturating wall at the circumference thereof in a rearward direction and having a major cylindrical portion adjacent the obturating wall that, at a location remote from said wall, steeply or abruptly increases in diameter to an enlarged circumferential end portion, said skirt or flange being slidably received within the container, and the circumferential end portion being more readily movable past said burr in a direction of movement in which the skirt or flange follows the obturating wall, as when the piston is inserted obturating-wall-first into said open end, than in the opposite direction, in which movement of the piston is substantially obstructed by said burr to inhibit removal of the piston from the container. 